The invention provides: for a process for preparing pulverulent polymers by drying aqueous polymer dispersions in the presence of copolymers based on ethylenically unsaturated C3-C6 carboxylic acids and their hydroxyalkyl esters as assistants; polymer powders obtainable by this process; aqueous polymer dispersions obtainable by free-radical aqueous emulsion polymerization of ethylenically unsaturated monomers in the presence of the novel copolymers, and the powders obtainable therefrom, and a polymeric binder as well as and mineral building materials which comprise the novel polymer powders.